1. Field of the Invention
The present invention relates to the field of artificially assisting heart function. More particularly, the invention relates to a device and a method for electromagnetically assisting the function of the ventricles in the heart.
2. Description of the Related Art
Despite the significant progress in prevention and medical treatment of cardiovascular disease, congestive heart failure (CHF) affects about 1 percent of adults in the United States (i.e. approximately 4-5 million patients), with 400,000 new cases occurring each year. CHF is the primary diagnosis for about 1 million hospitalizations each year and is a contributing factor in over 250,000 deaths annually. The age-adjusted death rate from CHF is 106.4 per 100,000. The median survival, after diagnosis, is 1.7 years for men and 3.2 years for women; the five year survival rate is less than 50 percent. It is estimated that nearly 60,000 patients annually in the United States could benefit from heart transplantation or long-term mechanical support. Evaluation and care of CHF patients costs our society in excess of $11 billion each year.
Currently, heart transplantation is considered the most effective therapy for end-stage CHF. However, heart transplantation presents multiple problems, including: (1) a shortage of donor hearts; (2) a significant perioperative morbidity/mortality rate; (3) the requirement of immune suppression; and (4) a less than ideal long-term survival rate. Accordingly, there is a crucial need for the development of alternatives to heart transplantation.
Mechanical support by means of implantable ventricular assist devices presently is the most promising alternative to heart transplantation. Currently available assist devices include extracorporeal oxygenators, univentricular and biventricular extracorporeal devices, and total artificial hearts. Most of these devices require the patients to be connected to cumbersome drive systems which makes their use limited only to hospital in-patients.
Lately, the development of an implantable left ventricular assist device (LVAD) and the development of wearable power supplies for this device has made the following possible: (1) a patient""s rehabilitation; (2) unrestricted patient mobility; (3) patient discharge to the home; and (4) a patient""s ability to return to work. However, while an LVAD may have some advantages over heart transplantation, an LVAD still presents many serious limitations for long-term use. These limitations include: (1) selection of patients (i.e., an LVAD is only available to patients without end-organ failure and qualification for an LVAD is as restricted as heart transplantation); (2) an LVAD is unavailable for patients on long-term glucocorticoid therapy or patients with a small body surface area; (3) it is difficult to assess a patient""s ability to manage an LVAD; (4) early post-operative complications such as bleeding, right heart failure, air embolism, and multiple organ failure are possible; and (5) late post-operative complications such as infection, thromboembolism. In addition, most LVADs are designed to assist systolic pumping ability only whereas impairment of diastolic relaxation ability is a major component of CHF.
For these and other reasons, a new device is needed which can assist systolic and diatolic function of the ventricles, which is available to a wide variety of patients, and which does not cause at least some of the early and late post-operative complications previously mentioned.
A virtual ventricular assist device (VVAD), herein disclosed, is designed to overcome many of the aforementioned limitations of an LVAD. For long-term use, the VVAD: (1) can assist systolic pumping and diastolic relaxation of CHF patients without structural defects (i.e., congenital or acquired valvular diseases); (2) requires no major surgery to implant and, therefore, avoids the early complications mentioned above; (3) requires no foreign materials to interact with the surface of the ventricular cavity or conduit vessels and, therefore, avoids the late complications mentioned above; (4) can be used for the right as well as the left ventricle; and (5) eliminates the need for anticoagulants.
The VVAD consists of essentially two components: (a) implantable magnetic pellets implanted through a delivery catheter; and (b) an external electromagnetic device which, when cyclically charged, attracts or repels the pellets depending on their corresponding charge. The term xe2x80x9cpelletxe2x80x9d is not to be limited to ball shaped materials; it is to be construed to include many other shapes including that of a plate or umbrella. Moreover, the pellets are xe2x80x9cmagneticxe2x80x9d in the sense that they react to magnetic fields in a manner similar to metals due to the presence of free electrons which orient themselves in response to a magnetic field; the pellets themselves are not charged.
The implantable pellets are spring-winged, contain materials which are responsive to magnetic fields, and are vacuum-sealed within a polyurethane membrane (or any other biologically inert, synthetic material). The pellets have a myocardial wall contact portion to which a plurality of wings is hingedly connected. Preferably, the pellets are deployed percutaneously to the mid-layer of the targeted myocardial wall through a major artery using a delivery catheter. It is also possible to implant the pellets through the chest wall and into a mid-layer of the targeted myocardium; this transthoracic implantation requires a minimally invasive surgical procedure using a thoracic endoscope. It is also possible to fix the pellets to the outside of the myocardial wall. Pellets made of diamagnetic metals (e.g., bismuth or antimony) are implanted in or on the posterior wall of the left ventricle (LV) whereas pellets made of ferromagnetic metals (e.g., iron or cobalt) are implanted in or on the anterior wall of the left ventricle. The shape of the pellet will depend on the location in which they are fixed and by the method by which they are introduced into the ventricle. For example, in a transthoracic approach, the implantable magnetic pellets can be plate shaped or umbrella shaped like a shell so that they can be implanted on the surface of the targeted myocardium.
The external electromagnetic device (which is battery operated and light enough to be worn in the chest wall) generates an electromagnetic force which is synchronized with an EKG, at least one lead of which monitors the user""s heart rate. This electromagnetic device may be external or internal to the chest wall. Onset of the force corresponds to the EKG""s R wave whereas offset of the force corresponds to the EKG""s T wave. Due to the charge of the electromagnetic field, pellets implanted in the posterior wall of the left ventricle will be pulled toward the electromagnetic device while the pellets in the anterior wall of the left ventricle will be correspondingly pushed away from the electromagnetic device. Due to this opposite motion, a compression of the left ventricle occurs. When the electromagnetic field is discontinued (due to the occurrence of the EKG T wave), the anterior and posterior walls of the left ventricle (which hold the magnetic pellets) return to their original positions. In this fashion, a cyclical compression of the left ventricle occurs thereby allowing the left ventricle to beat as if it were normal and healthy. This synchronized generation of electromagnetic force is designed to boost systolic pumping only during the early half of systole. Moreover, the magnitude of the electromagnetic force generated and its domain are adjusted to boost systolic function by 10-20 percent.
Pellets are implanted into the myocardium after being introduced into the body via a delivery catheter. The delivery catheter contains a mobile electromagnetic rod which is approximately 7 mm in length. The delivery catheter (preferably size 7 FOD, 120 cm) can be introduced into the body by means of a introducer catheter set which can be any commercially available percutaneous introducer set of size 8 F. If the delivery catheter can be introduced percutaneoulsy through a femoral artery, it is guided into the left ventricle by an external magnetic system working in conjunction with a fluorscope. In the alternative, the delivery catheter can be introduced through a transthoracic-epicardial route; this is a video-assisted method in which the pellets are implanted trans-epicardially into the targeted myocardium.
A spring-winged pellet is attached to the distal end of the electromagnetic rod. A wire (within the catheter) connects the proximal end of rod to an electromagnetic power generator and thereby supplies current to the rod; the current charges the electromagnetic rod thereby creating an electromagnetic field around the rod. The electromagnetic field causes the wings of the spring-winged pellet to overcome their otherwise extended orientation and thereby to collapse on the electromagnetic rod. The pellet is maintained in this fashion until it is positioned within the myocardium. When the pellet (attached to the catheter tip) is positioned against the targeted myocardial wall position, the catheter tip is forcefully anchored against the endo-myocardial wall by an external magnet. An injection syringe then hydraulically forces the rod with the pellet into the myocardium. When the pellet is placed within the myocardium, the current supplied to the electromagnetic rod via the wire is discontinued causing the wings to open thereby preventing the pellet from travelling backwards (i.e., in the direction of the delivery catheter when the catheter is removed). After the wings have opened, the rod is hydraulically pulled back into the catheter which is then removed from the body.
In this fashion, pellets should be deployed one at a time. In addition, 3 or 4 pellets (or as many as needed) should be positioned in each ventricular myocardial wall (i.e., anterior and posterior) and should be distributed to cover 6-15 square cm of myocardial area.
The present invention includes a novel magnetic spring-winged pellet, a method of inserting the pellet, and a method of treating congestive heart failure using spring-winged pellets implanted in or on the myocardial walls of a ventricle in conjunction with an external electromagnetic field generator.
One embodiment of the spring-winged pellet includes: (a) a contact portion; and (b) a plurality of wings. In this embodiment each wing has a distal end portion hingedly connected to the contact portion and each wing has a proximal end portion which bends toward the proximal end portions of the other wings when an electromagnetic field is applied to the pellet.
One method of inserting a magnetic pellet into a myocardial wall of a heart includes: (a) supplying an electromagnetic field to the pellet which has a plurality of spring-wings and which is attached to a distal end of an electromagnetic rod which is positioned within a delivery catheter; (b) positioning the magnetic pellet at a target area on the myocardial wall; (c) using an injection syringe positioned at a proximal end of the catheter to force the pellet into the myocardial wall; and (d) removing the electromagnetic field previously supplied to the pellet and thereby causing the spring-wings to open. Preferably, the myocardial wall into which the pellets are inserted is in the heart""s left ventricle. Moreover, the wall can be either a posterior wall or an anterior wall of the left ventricle. However, the pellets may also be inserted into the myocardial wall of the right ventricle wall using a transthoracic insertion. The electromagnetic field is preferably created by external electromagnetic generator which is electrically connected to a proximal end of the electromagnetic rod by a wire. Finally, this method can be practiced by introducing the delivery catheter to the target area of the myocardial wall by sending the catheter through a femoral artery or by transthoracically sending the catheter through a chest wall.
A preferred method of treating a patient""s congestive heart failure includes: (a) positioning a first plurality of magnetic spring-winged pellets in a myocardium of posterior wall of a ventricle of a heart; (b) positioning a second plurality of magnetic spring-winged pellets in a myocardium of an anterior wall of a ventricle of a heart; (c) using an electromagnetic generator to cyclically generate an electromagnetic field which magnetically interacts with the first and the second plurality of pellets; (d) magnetically pulling, in response to the cyclical electromagnetic field, the first plurality of pellets toward the electromagnetic generator; and (e) magnetically pushing, in response to the cyclical electromagnetic field, the second plurality of pellets away from the electromagnetic generator. Ideally, this method also includes: (f) positioning an EKG monitor on the patient and generating a waveform of the heart""s electrical activity; and (g) synchronizing the cyclical electromagnetic field to correspond to the heart""s electrical activity.
A method is also provided to aid in the compression and relaxation of a heart chamber (which may be the heart""s left ventricle) of a patient. This method includes: (a) inserting a plurality of ferromagnetic pellets into the anterior wall of the heart chamber and inserting a plurality of diamagnetic pellets into the posterior wall of the heart chamber; (b) positioning a first electromagnetic field generator on the chest wall of the patient and a second electromagnetic field generator on the back wall of the patient; (c) generating a first electromagnetic field with the first electromagnetic field generator thereby pushing the ferromagnetic pellets in the anterior wall away from the first electromagnetic field generator and pulling the diamagnetic pellets in the posterior wall toward the first electromagnetic field generator to compress the heart chamber; (d) discontinuing the first electromagnetic field generated by the first electromagnetic field generator; (e) generating a second electromagnetic field with the second electromagnetic field generator thereby pulling the diamagnetic pellets in the posterior wall toward the second electromagnetic field generator and pushing the ferromagnetic pellets in the anterior wall away from the second electromagnetic field generator to relax the heart chamber; and (f) discontinuing the second electromagnetic field generated by the second electromagnetic field generator. The steps of creating the electromagnetic fields to compress and relax the heart chamber are then cyclically repeated. In addition, this method may also include: (g) positioning an EKG monitor on the patient and generating a waveform of the heart""s electrical activity; and (h) synchronizing the cyclical electromagnetic fields generated by the first and second electromagnetic field generators to correspond to the heart""s electrical activity. This method can also be performed by placing the ferromagnetic pellets in the posterior wall and the diamagnetic pellets in the anterior wall, provided, however, that the electromagnetic field generators are corresponding switched.
These and other features, aspects, and advantages of the present invention will become more apparent from the following description, appended claims, and accompanying exemplary embodiments shown in the drawings.